1. Field of the Invention
The present invention relates to a fuel cell having a plurality of power generation units arranged in a same plane. Each of the power generation units includes an anode, a cathode, and an electrolyte interposed between the anode and the cathode. Further, the present invention relates to a method of producing the fuel cell, and a fuel cell stack including a plurality of the fuel cells.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes two electrodes (anode and cathode), and an electrolyte membrane interposed between the electrodes. Each of the electrodes comprises an electrode catalyst layer of noble metal supported on a carbon base material. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is a power generation unit interposed between separators (bipolar plates). The membrane electrode assembly and the separators make up a unit of a fuel cell (unit cell) for generating electricity. A predetermined number of the fuel cells are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas (reactant gas) such as a gas chiefly containing hydrogen (hydrogen-containing gas) is supplied to the anode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions (protons) and electrons. The hydrogen ions move toward the cathode through the electrolyte, and the electrons flow through an external circuit to the cathode, creating a DC electric current. A gas chiefly containing oxygen (oxygen-containing gas) or air is supplied to the cathode. At the cathode, the hydrogen ions from the anode combine with the electrons and oxygen to produce water.
For example, Japanese Laid-Open Patent Publication No. 2002-56855 discloses a flat fuel cell in which a plurality of unit cells are arranged in the same plane in a single row, or a plurality of rows. The unit cells are electrically connected in series.
FIG. 23 shows the flat fuel cell. The flat fuel cell includes unit cells 4a through 4d. Air electrodes (cathodes) 2a through 2d and fuel electrodes (anodes) 3a through 3d are provided on both sides of electrolyte layers 1a through 1d. The same electrodes are arranged on the same side of the electrolyte layers 1a through 1d, i.e., the cathodes 2a through 2d are arranged on one side of the electrolyte layers 1a through 1d, and the anodes 3a through 3d are arranged on the other side of the electrolyte layers 1a through 1d. Conductive Z-like connection plates 5a through 5d connect the unit cells 4a through 4d together in series.
Specifically, the conductive Z-like connection plate 5a connects the cathode 2a of the unit cell 4a and the anode 3b of the unit cell 4b, the conductive Z-like connection plate 5b connects the cathode 2b of the unit cell 4b and the anode 3c of the unit cell 4c, and the conductive Z-like connection plate 5c connects the cathode 2c of the unit cell 4c and the anode 3d of the unit cell 4d. The anode 3a of the unit cell 4a is connected to a terminal 6a, and the cathode 2d of the unit cell 3d is connected to a terminal 6b. 
According to the disclosed prior art technique, the dedicated Z-like connection plates 5a through 5c are required for connecting the cathodes 2a through 2d and the anodes 3a through 3d of the unit cells 4a through 4d electrically in series. The Z-like connection plates 5a through 5c extend between the cathodes 2a through 2d and the anodes 3a through 3d, respectively. In this structure, the reliable sealing performance between the cathodes 2a through 2d and the anodes 3a through 3d may not be achieved.
Moreover, the thickness of the fuel cell in the direction indicated by an arrow T is large. Thus, the overall size of the fuel cell is not small.
Further, the thickness of the fuel cell indicated by an arrow T is large. Thus, the overall size of the fuel cell is not small. Further, the unit cells 4a through 4d are separate components. Therefore, the unit cells 4a through 4d may not be positioned accurately in alignment with each other.
If the fuel cell stack is mounted on a vehicle, two hundreds to six hundreds of unit cells are required to form the fuel cell stack for generating the desired level of voltage and current for driving the vehicle. In the disclosed prior art technique, preferably, a plurality of the flat fuel cells may be connected in series for generating a high level of voltage.
When the fuel cells are stacked together for generating a large electrical energy at a high voltage, the excessive heat generation of the fuel cells may affect the performance of the fuel cell stack. Therefore, it is essential to use a liquid cooling system for effectively cooling the fuel cells. However, Japanese Laid-Open Patent Publication No. 2002-56855 merely discloses a fuel cell operated at a small voltage. No solutions using such a cooling system are suggested in the disclosure.